Cathode ray deflecting device



y 9, 1939- l. G. MALOFF 2,157,182

CATHODE RAY DEFLECTING DEVICE Filed Dec. 51, 1935 2 Sheets-Sheet l W 5 JWQVQYLZW Z 5 g J May 9, 1939. 1, 5 MALOFF 2,157,182

CATHODE RAY DEFLECTING DEVICE Filed Dec. 51, 1935 2 Sheets-Sheet 2 fnzzcn/ior baggy fiwff Patented 9, 1939 PATENT OFFICE 2,157,182 csrnonr: an nsrwormc 'nsvrcn Ioury G. Malofl, Philadelphia, Pa., assignor to Radio Corporation of America," a corporation of Delaware Application December 31, 1935, Serial No. 56,843;

3 Claims.

My invention relatesto'cathode ray tube deflecting devices and particularly to deflecting devices of the electromagnetic type.

'In the past, deflecting devices of theabovementioned type have not been very satisfactory 1 receiver, in particular, it is desirable to deflect the cathode ray through a rather large angle;

The deflection in one standard size television receiver tube'provided with electromagnetic deflection is'suflicient to produce a picture seven or is eight inches square. Because of defocusing of the cathode ray, however, the outer edges of the picture are not sharply defined unless special precautions are taken for reducing defocusing. A further difllculty encountered in utilizing o electromagnetic deflection is that, when the cathode ray is caused to scan a fluorescent screen (as by means of vertical deflecting and horizontal deflecting saw-tooth waves), the pattern on the screen is likely to be distorted. The greater the 2 angle of deflection, the greater is'this distortion. The pattern distortion may be of such a. character as to reproduce a circle as a square with rounded corners.

It is an object of my invention to providean a improved electromagnetic deflecting device for cathode ray tubes. e

It is a further object of my invention to provide a method of and. means for reducing defocusing of a cathode ray.

It is a still further object of my invention to provide a method of and means for reducing distortion in the scanning pattern of a cathode ray tube.

In practicing my invention, I provide a de- 40 fleeting fleld which has a more uniform, flux distribution in the plane perpendicular to the undeflected electron beam than deflecting flelds previously produced by deflecting coils. In oneembodiment of the invention, this increase in flux uniformity ismbtained by properly positioning is constructed in accordance with-one embodiment of my invention; a e

permanentrmagnets adjacent to the deflecting;

Fig. 2 is an end view of the deflecting yoke shown in Fig. l;

Figs. 3a to 3h are diagrams showing the flux distribution produced by a deflecting yoke of the conventional type, and Figs. 4a to 4% are diagrams showing the flux distribution produced by the deflecting yoke shown in Figs. 1 and 2.

Referring to Fig. 1, my deflecting yoke is shown mounted on a cathode ray tube of a conventional 0 type. The cathode ray tube comprises an evacuated envelope I having therein an electron gun 2 and a fluorescent screen 3. A metallic coating- 4 on theinner surface of the envelope functions as the SGQQIld anode and also provides an elecl5 trostatic field next to the electron gun 2 forfocusing the cathoderay.

Referring to Figs 1 and 2. the deflecting yoke comprises a magnetic coreor ring 6, this core preferably being built up of softiron laminations which are clamped between two iron rings I and 8. Two diametrically opposed pole pieces 9 and II of magnetic material extend from the inner periphery of the core 6, these pole pieces having a pair of horizontal deflecting coils l2 and I3 mounted thereon. 1

At right angles to the pole pieces 9 and I I, two other diametrically opposed pole pieces I4 and I8 extend from the core 6, these pole pieces having the vertical deflecting coils l1 and I8 mounted thereon. Terminal lugs l9, 2i, 22 and 23 for the deflecting coilsare mounted on brackets ex-' tending from thering-I.

The deflecting yoke so far described istone which is well known in the art, each pair of coils being connected in series-aiding relation. For the reasons previously mentioned, it is not very satisfactory if the cathode ray tube is to be employed in a television system. The shapes of the magnetic fields produced by this yoke under several different conditions of deflection as indicated by iron filings-are shown in Figs. 3a to 311.. In these figures the letters N and S indicate the polarity of the deflecting coils for the several conditions of deflection.

In accordance with my invention, I change the shape of the magnetic field to make it more uniform in the region through which the cathode ray is deflected and in a plane at right angles to the axis of the electron gun or undeflected oathode ray. I have found that this can be accomplished by employing magnets such as permanent magnets properly positioned with respect to the ends of the pole pieces.

.In ggai and 2, four permanent magnets 24; u

28, 21 and 28 are shown, one magnet being provided for each pole piece. The permanent magnets. are supported by brackets 29, 3|, 32 and 33 extending from the iron ring 1, these brackets as well as the clamping members 34 being. of magnetic material whereby a good magnetic circuit is provided from the magnets through the core 8.

In the specific embodiment illustrated, each permanent magnet is mounted with its north end adjacent to the end of its corresponding pole piece and with its axis ,at an angle of approximately 22 to the axis of the said pole piece.

The shapes of the magnetic fields produced by this improved structure for diflerent conditions of deflection are shown in Figs. 4a to 4h. In these figures the circle indicates approximately the area through which the cathode ray is deflected. It will be noted that the improved deflecting yoke provides a magnetic field in which the variation in flux density from point to point in the area through which the cathode ray is deflected is less than in the case of the old type of yoke. As a; result, in the plane of the pole pieces, that is in the plane of the paper in Figs. 4a to 4k, the flux may of the magnetic field is comparatively uniform throughout the region traversed by the cathode ray during deflection. Consequently, there is a reduction in defocusing of the cathode ray and in distortion of the deflection pattern on the fluorescent screen.

It will be understood that various modifications may be made in my invention without departing from the spirit and scope thereof, and

I desire, therefore, that only such limitations shall be imposed thereon as are necessitated by the prior art and are set forth in the appended claims.

I claim as my invention:

1 In combination with a cathode ray tube having an electron gun, means including de-. flecting coils for producing a magnetic .deflect ing field, and additional means for making said field substantially uniform from point to point in a plane at right angles to the axis of said gun, said additional means comprising a plurality of permanent magnets adjacent said deflecting coils and developing a magnetic field correcting non-uniformity. in said deflecting field.

2. A deflecting device for cathode ray tubes in which a cathode ray is produced, a pair of oppositely disposed deflecting-coils having a magnetic circuit which is closed except for an air gap in which a cathode ray tube may be located, a second pair'of oppositely'disposed deflecting coils located at right angles to said first coils and having a magnetic circuit a portion of which is common to said first magnetic circuit, a plurality of magnets adjacent said deflecting coils each having a north pole and a south, one of said magnets being so positioned adjacent to each of said coils that the deflecting field produced thereby is made substantially uniform from point to point in a plane at right angles to the undeflected cathode ray.

3. A deflecting device for cathode ray tubes, said device comprising a magnetic core having oppositely disposed pole pieces, there being an air gap between said pole pieces in which a cathode ray tube may be placed, a pair of deflecting coils mounted on said pole pieces and connected to produce a deflecting field in said air gap, and a plurality of auxiliarymagnets adjacent said deflecting coils, at least one magnet being so positioned adjacent to each of said pole pieces that the said deflecting field is made substantially uniform.

IOURY G. MALOFF. 

